[sdiy] Shielding

[Ingo Debus]

Moho Disco wrote:
> Currently I'm just using the laptop's crappy internal soundcard, which
> is wired directly into my Mackie 1604vlz.  A laptop adapter for my
> Layla24 sound card should be arriving Monday, and I'm *praying* that
> it does not exhibit the same symptoms.
> 
> >If you remove all the wires, does the noise stop ?  (the idea is if the noise
> >stops... it is being conducted by some wiring, not through the air...)
> 
> Yep, the noise stops when I disconnect the cables from the computer
> to the mixer.  It is most definitely being conducted through a wire...
> But it doesn't matter what wire I use, they all transmit it.

Like Theo obviously suspects too, this is most likely a ground loop
problem. A friend of mine had that prob too with a Mackie mixer. It's
difficult to disconnect signal ground from protective earth in these
mixers without affecting electrical safety. All jacks are connected
directly to the case as well as the power transformer, power switch and
so on. An option is re-building the mixer's power supply into an
external case (larger DIY project). Another option is using DI boxes or
isolation transformers in the audio pathes between mixer and computer.
I don't know the Layla card, if it has assymetrical (unbalanced)
ins/outs the problem most likely won't go away :-(

Ingo